Arrangement for mounting filaments



Jan. 28, 1930. w.,N. MISCHL ER ARRANGEMENT FOR MOUNTING FILAMENTS Filed Sept. 18, 1928 Inventor: William N. Mischler,

H H15 Attorney.

Patented 1.... as, 11930 UNITED STATES PATENT OFFICE wmnnm ll. IISOHLER, O1 SOO'IIA, NEW YORK, ASSIGHOB G ELECTRIC COMPANY, A CORPORATION NEW YORK ARRANG'EIIEN'I FOB HOUNTING III-m8 Application filed September 18, 1988. Serial No. 808,780.

The present invention relates to electron discharge devices and in particular, to the construction of the filament electrode of such devices. In high power thermionic appa- 5 ratus, the filament which serves the functlon of emitting electrons may take the form of a double, reversely wound, helix, one spiral being a continuation of the other, and having their free ends sealed into the pres of the envelop. Due to the considerab e length of this member in high power tubes, the helix may tend'to sway or in other manner change the s acial relation with respect to the associate electrodes. It has been customary to provide a support in the form of a standard rising from the press which serves to maintain the upper ends of the filament in a centrally aligned position of the envelop, at the same time offering substantially no impedi- 20. ment to the normal expansion of the heated member in a longitudinal direction. In addition to the standard, it has been heretofore roposed to employ a collar or sleeve of reactory material, for example, tungsten, on both sides of the standard and to thread the last loop of each helix through the respective collars. The inner surfaces of these collars usually bear against the standard and the outer surfaces against the oppositely positioned convolutions, whereby the collars serve to space the helices equidistantly from the standard. It has been found, however, that this form of construction is expensive both in material and labor and accordingl I have devised a simple expedient which eliminates the use of collars but nevertheless maintains the equidistant relation between the double helix and the standard and hence between the filamentand the remaining electrodes. In

general, this end is attained by providing a small loop at the extreme end of the helix which fits over, and is held by the standard. An object of my invention is to devise an inexpensive filament construction of the double helix type. Another object is to provide a simple construction as will efl'ectively position a relatively long filament within an envelop and also allow free longitudinal movement of expansion. Other objects and advantages will be apparent as the specification is perused in connection with the accommetrically disposed flanges into which are secured rods 7 7, 7 7 sealed in said stems; two of the rods together may constitute a leading-in conductor. Concentrically arranged within the anode 6, there are two helical grid members 8 and 9, the former of which serves to control the flow of space current in the well-understood manner and is supported from the stem 4 by means of suitable conductors. The screen-grid 9 so-called is positioned between the control grid and the anode; this screen-grid serves to intercept the electrostatic lines of force extending between the control grid and the anode there by to preclude self-sustained radio frequency oscillations. The use of the screen-grid is disclosed and claimed broadly in an application of Albert W. Hull filed March 3, 1924, Serial No. 696,665 and assigned to the same assignee as the present invention. The re spective grid members may be formed on frameworks secured to the stems 4 and 5 in any suitable manner, for example, by a clamp or by scaling) in the glass, the lead for the control grid eing taken out throu h the cap 10 to a suitable terminal 11 and t at of the screen grid through the cap 12 to a terminal 13. For the 'sOurce of electrons, I provide a filament 14 of suitable metal, for example, tungsten in the form of a double helix which is centrally positioned with respect to the remaining electrodes and the ends of which are fused in the stem 5 in the manner shown.

Projecting from the stem 5, there is a standard or upright 15 of refractory metal, for example, tungsten which serves to maintain the axial position of the member 14. In order to effect this purpose, there is provided a'relatively small loop or turn 16 formed at the upper end of the filament, having an inner diameter slightly larger than the diameter of the u right so as to preclude friction about the sur ace of the latter. It will be evident that the loop effectively prevents any side wise movement of the filament 14 and hence, maintains the spacing between the filament and the various other electrodes, and at the same time allows free expansion and contraction of the heated member. The loop enables the last turn of the helix to take up any radial position depending upon the torsion in the double helix thereby preventing strain or distortion in the filament. In the event that the helical member is made of relatively small wire, there may be a tendency for this member to slide downwardly along the standard, in which case a projection may be formed on the standard 15 just below the loop portion of the filament as for example by a spot weld, although ordinarily, such projection has been found to be unnecessary. The loop may be formed in any suitable manner but I have found it expedient to provide a mandrel in which there has been cut a double helical thread and having a small pin projecting at the end of the mandrel around which th filament is tightly wound to form the loop 16 immediately after the first helix is completed and prior to beginning the formation of the reversely wound helix. It is apparent that the operation of constructing the loop is exexceedingly simple and that its assembly on the upright 15 represents a very small item of labor, thus the cost of the finished tube is materially less than when the collar form of support is employed.

While I have explained the invention in connection with high power screen-grid amplifier, it is evident that it has application to all forms of electron discharge devices, oscillators, rectifiers and the like which may utilize the double form of helical filament to advantage and the length of which is such as to require a support at the end remote from the press.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In an electron discharge device, an evacuated envelop having a stem, a filament supported from said stem and spaced from a cooperating electrode, said filament being of such size and length as may cause a change in the electrode spacing under operating conditions and means for maintaining the normal spacing, said means comprising a small loop at the end of the filament remote from the stem and including a device for slidably positioning the loop within the envelope.

2. In an electron discharge device, an evacuated envelop having a stem, a filament supported from said stem and spaced from a cooperating electrode, said filament being of such size and length as may cause a change in the electrode spacing under operating conditions and means for maintaining the normal spacing, said means comprising a small loop at the end of the filament remote from the stem and a rod rigid] aflixed at one end anal threaded through said loop at the other en 3. In an electron discharge device, an evacuated envelophaving a stem, a filament supported from said stem and spaced from a cooperating electrode, said filament being of such size and length as may cause a change in the electrode spacing under operating conditions and means for maintaining the normal spacing, said means comprising a small loop at the end of the filament remote from the stem and a rod rigidly afiixed at one end to said stem and threaded through said loop at the other end.

4. In an electron discharge device, an evacuated envelop having a stem, a double helical filament secured in said stem and provided with a loop, a standard aflixed in said stem and threaded through said loop whereby the filament is rigidly maintained in its desired position.

In witness whereof, I have hereunto set my hand this 17th day of September, 1928.

WILLIAM N. MISCHLER. 

